A double layer cooler of the aforementioned generic type is known for example from DE-C-10 97 346. Such a cooler has the advantage that the cooling surface, which consists for example of grate plates and/or rows of grate plates which can be aerated individually, is protected from heat since the lower layer is already precooled and thus acts as a protective layer.
However, such a construction has the disadvantage that with fluctuating quantities of recirculated material the height of the lower layer also varies constantly. This results on the one hand in difficulties in adjusting the separating arrangement at the end of the cooler, so that in certain circumstances material which has already cooled sufficiently is returned as recirculated material and on the other hand the cooling effect varies due to the differing layer heights of the lower layer.
The object of the invention, therefore, is to construct a double layer cooler of the type mentioned in the introduction so that the efficiency of the cooler is improved.